This project seeks to unravel the functional organization of multiple maps in the auditory cortex of higher mammals and thus to improve our understanding of the neural basis for acoustic communication. compared to visual and somatosensory cortex, our knowledge about the organization of auditory cortical areas and their thalamic inputs is much poorer. We are analyzing single unit responses to auditory stimuli in different auditory fields of cats and macaque monkeys. In addition to pure tones, we use standardized complex sounds for stimulation. Neurons in the anterior areas of the cat's auditory cortex respond best to highly transient stimuli with a fast rate of frequency modulation and are often spatially tuned, whereas the posterior areas show a tendency to respond better to slow modulations. In monkeys, a similar approach has been taken to explore the multiple maps in nonprimary auditory cortex. Neurons in the rostro-lateral area (RL) respond preferentially to low-frequency sounds, as they are contained in communication signals. By contrast, neurons in the caudo- medial area (CM) prefer high frequencies, which are important for sound localization. Lesioning of primary auditory cortex (Al) abolishes tonal responses in area CM but not in RL. Tracer injections into matched frequency representations in these two areas reveal different inputs from the medial geniculate nucleus (MGN) of thalamus. While RL (like Al) receives direct input from the main nucleus (the ventral division) of the MGN, CM gets input only from its dorsal division and thus depends more on input from Al for its responsiveness. This shows that auditory information is relayed both serially and in parallel from the thalamus to the auditory cortex.